Classification of Wetlands and Deepwater Habitats of the United States

Reef

Definition. The Class Reef includes ridge-like or mound-like
structures formed by the colonization and growth of sedentary
invertebrates. Water regimes are restricted to subtidal,
irregularly exposed, regularly flooded, and irregularly flooded.

Description. Reefs are characterized by their elevation above
the surrounding substrate and their interference with normal wave
flow; they are primarily subtidal, but parts of some reefs may be
intertidal as well. Although corals, oysters, and tube worms are
the most visible organisms and are mainly responsible for reef
formation, other mollusks, foraminifera, coralline algae, and
other forms of life also contribute substantially to reef growth.
Frequently, reefs contain far more dead skeletal material and
shell fragments than living matter.

Subclasses and Dominance Types.

Coral. -- Coral Reefs are widely distributed in shallow waters of
warm seas, in Hawaii, Puerto Rico, the Virgin Islands, and
southern Florida. They were characterized by Odum (1971) as
stable, well-adapted, highly diverse, and highly productive
ecosystems with a great degree of internal symbiosis. Coral Reefs
lie almost entirely within the Subtidal Subsystem of the Marine
System, although the upper part of certain Reefs may be exposed.
Examples of Dominance Types are the corals Porites, Acropora, and
Montipora. The distribution of these types reflects primarily
their elevation, wave exposure, the age of the Reef, and its
exposure to waves.

Mollusk. -- This Subclass occurs in both the Intertidal and
Subtidal Subsystems of the Estuarine System. These Reefs are found
on the Pacific, Atlantic, and Gulf Coasts and in Hawaii and the
Caribbean. Mollusk Reefs may become extensive, affording a
substrate for sedentary and boring organisms and a shelter for
many others. Reef mollusks are adapted to great variations in
water level, salinity, and temperature, and these same factors
control their distribution. Examples of Dominance Types for this
Subclass are the oysters Ostrea and Crassostrea (Smith 1964;
Abbott 1968; Ricketts and Calvin 1968).

Worm. -- Worm Reefs are constructed by large colonies of
Sabellariid worms living in individual tubes constructed from
cemented sand grains. Although they do not support as diverse a
biota as do Coral and Mollusk Reefs, they provide a distinct
habitat which may cover large areas. Worm Reefs are generally
confined to tropical waters, and are most common along the coasts
of Florida, Puerto Rico, and the Virgin Islands. They occur in
both the Intertidal and Subtidal Systems of the Marine and
Estuarine Systems where the salinity approximates that of sea
water. The reefworm Sabellaria is an example of a Dominance Type
for this Subclass (Ricketts and Calvin 1968).